Soaring fuel costs, global warming and other economic factors have made vehicle weight reduction a priority in the automotive industry in an effort to maintain customer satisfaction. These demands need to be made without compromising vehicle safety, necessitating finding a proper balance to satisfy all requirements. Grey iron steel has long been traditionally used in the manufacture of automotive brake rotors. While this application material has an expected performance satisfactory to industry standards, it offers limited opportunities for optimizing weight reduction and improved performance. Other attempts have been made to produce a brake rotor using lighter weight materials, accomplishing weight reduction goals only at the expense of cost and performance. This invention describes a disc brake rotor for a motor vehicle, made using conventional aluminum and steel materials and unique methods resulting in a light weight product with improved performance advantages over prior art.
It is known that rotors cast entirely from an aluminum alloy material possess strength deficiencies as temperatures elevate during normal braking use. Relatively thin wear inserts made of a suitably hard material such as steel encapsulated within the aluminum at the friction surfaces in contact with typical brake pads are capable of maintaining required strength under these conditions. Aluminum has known thermal conductivity properties superior to that of grey iron steel traditionally used in the manufacture of brake rotors, providing performance improvements from expected operation as friction heat is rapidly transferred from the steel inserts into the aluminum and then dissipated to air.
U.S. Pat. No. 5,620,042 by Ihm discloses a composite brake rotor, with friction surfaces made from metal matrix composite (MMC), an aluminum based material that includes silicon carbide particulate for reinforcement, and the rotor body made from conventional aluminum alloy.
U.S. Pat. No. 5,862,892 by Conley discloses a brake rotor made from aluminum combined with cast iron wear surfaces.
These disclosed rotor designs may have inherent problems. Metal matrix composite materials are expensive and very difficult to machine, making them cost prohibitive. In addition, special organic brake pads are required to be used for compatibility with the MMC material to prevent galling damage to the rotor surfaces. These pads are also more expensive when compared to conventional pads used with cast iron rotors, due to their material makeup and availability. And because they are made up mostly of aluminum, they have lower overall operating temperature potential. Smearing of the aluminum is also known to occur as the brake friction force exceeds the shear strength of the MMC material. Coefficient of thermal expansion differences can cause detrimental warping and separation problems on composite rotors made from both aluminum and cast iron or steel. The rotor disclosed by Conley uses cast iron wear surfaces that are interconnected to one another, limiting heat dissipation.
The present invention details the use of materials and methods to address these concerns. Material and labor cost concerns are managed by means of the use of commercially available grades of aluminum and steel. These materials have properties that promote ease of machining by cost effective conventional methods. This invention allows the use of common, commercially available mating brake pad components. The invention also describes a practical approach to solving warp and separation that may develop between the dissimilar materials. Slots are spaced radially around the steel wear inserts to allow adequate expansion to occur as temperatures elevate during normal brake use.
A suitable method of attaching the wear inserts to the aluminum rotor body is also described. Prior art methods for joining one metal to a second metal have been disclosed.
U.S. Pat. No. 4,023,613 by Uebayasi, et al. discloses a method for making composite metal castings by forming a plurality of teeth in at least one of the opposed surfaces of the metals being joined.
U.S. Pat. No. 5,894,053 by Fried, et al. discloses a process for applying a metallic adhesion layer for ceramic thermal barrier coatings to metallic components.
U.S. Pat. No. 7,066,235 by Huang discloses a method for manufacturing clad components that could be used for making an automotive brake rotor.
Inherent problems confronting the disclosed methods include cost to produce and accuracy. Processes for adding or attaching interlocking members add cost and must be tightly controlled to ensure robustness and repeatability from part to part in order to produce a rotor that meets rotating mass balancing requirements. In addition, hard spots can develop where the interlocking members join with the steel clad wear surface part due to process variables during heat treatment. The resulting hardness variations in the steel clad wear surfaces negatively affect brake wear performance.
The present invention describes alternative methods and design approaches that includes reliably and accurately adding interlocking members to one of the metals, and alternatively making one of the metals as a unitary part that includes the interlocking members